EP0162599B1 - Level control for a fluidized bed - Google Patents
Level control for a fluidized bed Download PDFInfo
- Publication number
- EP0162599B1 EP0162599B1 EP85302874A EP85302874A EP0162599B1 EP 0162599 B1 EP0162599 B1 EP 0162599B1 EP 85302874 A EP85302874 A EP 85302874A EP 85302874 A EP85302874 A EP 85302874A EP 0162599 B1 EP0162599 B1 EP 0162599B1
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- EP
- European Patent Office
- Prior art keywords
- bed
- particles
- tube
- coating
- weir
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
- B01J8/1809—Controlling processes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05C19/00—Apparatus specially adapted for applying particulate materials to surfaces
- B05C19/02—Apparatus specially adapted for applying particulate materials to surfaces using fluidised-bed techniques
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D1/00—Processes for applying liquids or other fluent materials
- B05D1/18—Processes for applying liquids or other fluent materials performed by dipping
- B05D1/22—Processes for applying liquids or other fluent materials performed by dipping using fluidised-bed technique
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
- B05D7/24—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials for applying particular liquids or other fluent materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/00017—Controlling the temperature
- B01J2208/00389—Controlling the temperature using electric heating or cooling elements
- B01J2208/00407—Controlling the temperature using electric heating or cooling elements outside the reactor bed
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/00548—Flow
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/0061—Controlling the level
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S118/00—Coating apparatus
- Y10S118/05—Fluidized bed
Definitions
- This invention relates to level control and, more particularly, to a method and apparatus for maintaining a predetermined upper level in a fluidized particle bed.
- pyrolytic carbon coatings on certain objects.
- uranium particles can be coated with a pyrolytic carbon which, in part, forms a pressure-retentive shell allowing the coated particles to be fabricated into fuel rods for use in nuclear reactors.
- Another important use for such coatings is for heart valve and other biomedical components because a pyrolytic carbon coating does not react with blood.
- Pyrolytic carbon is usually deposited on an object by thermally decomposing gaseous hydrocarbons or other carbonaceous substances in vaporous form in the presence of the object.
- one of the variables upon which the structure of the pyrolytic carbon will be dependent is the amount of available deposition surface area relative to the volume of the furnace enclosure wherein the deposition is occurring.
- Pyrolytic carbon which has a microstructure that has smaller growth features will be deposited when the relative amount of deposition surface area is fairly high. Thus, when relatively large objects, for example, objects having at least one dimension equal to 5 mm.
- an ancillary bed of small particles (usually of a size meaasured in microns) is included within the furnace enclosure together with the larger objects.
- This arrangement provides sufficient available total surface area to assure that pyrolytic carbon having the desired crystalline form will be deposited.
- the random motion of large objects in fluidized beds provides for a relatively uniform deposition of carbon on all surfaces.
- the total surface area of the particles begins to increase significantly as the diameters of the pyrolytic carbon-coated particles grow.
- This change in the available deposition surface area in the fluidized bed will result in a change in the physical characteristics or the pyrolytic carbon being deposited if the other coating variables are held constant, e.g., coating temperature, gas flow rate and gas composition; and moreover, when the bed reaches some maximum size, it will collapse and thus limit the thickness of the carbon coating that can be deposited on levitated substrates under constant input conditions. Changes in the physical characteristics of the carbon deposited may be undesirable for any of a number of reasons.
- the rate at which the particles are removed is controlled by regulating the rate of flow of an inert gas up the tube.
- the seed particle input is at a constant rate and the output is measured so that by varying the purge gas flow rate to regulate the output, a substantially constant bed total surface is achieved.
- the level control of the present invention operates to substantially eliminate dust from the particle discharge pipe for the bed apparatus, which dust otherwise could interfere with the collection of withdrawn particles.
- the level control also functions to reduce the ratio of smaller particles to larger particles being withdrawn to enhance the coating efficiency of the fluidized bed apparatus.
- the level control operates passively to achieve maintenance of a predetermined bed level, the complexity of the overall fluidized bed system is reduced because the need to weigh the output and input, and continually change a flow rate in response thereto is eliminated.
- the level control of the invention is reliable, has a long service life, and is simple to manufacture.
- the present invention provides a fluidized bed apparatus comprising an enclosure for containing a bed of the particles; means for causing flow of a gaseous atmosphere carrying a material for forming a coating of said particles upwards through the bed of particles to fluidize the particles, said coating having a relatively lesser density and said particles having relative greater densities; and a weir tube defined by a side wall, said means for causing flow of the gaseous atmosphere being adapted to cause the gaseous atmosphere to flow from underneath the bed and substantially centrally thereof, the weir tube being substantially vertically disposed and extending through a portion of the bed adjacent a side wall thereof; the means for causing flow of the gaseous atmosphere causing bubbling of the bed of particles above a predetermined level with the bubbling being generally confined to the central portion of the bed, which is characterised in that the weir tube extends above said bed and has a spillover entrance hole defining a maximum particle level for the bed by receiving and removing particles having substantial coatings from the bed but not removing substantial quantities
- the fluidized bed apparatus of the present invention includes an enclosure holding the bed of the particles and means for causing the upward flow of the gaseous atmosphere carrying a material for forming the coating through the bed of particles to fluidize the particles.
- a means for adding seed particles to the bed is provided, and a weir tube means removes coated particles from the bed when the content of the bed achieves a predetermined level.
- the apparatus includes a discharge means for removing the coated particles from the tube and conveying them to a collection location.
- fluidized bed apparatus for applying a pyrolytic carbon coating to objects, is generally indicated by reference character 20.
- the apparatus includes a furnace 22 having a cylindrical outer shell 24.
- the furnace shell 24 supports the coating enclosure which is defined by a tube 26 having an insert 28 affixed thereto at its lower end.
- the insert 28 provides the internal coating enclosure with conical bottom surface 30.
- a central passageway 32 extends vertically upward through the insert 28, coaxial with the tube 26, and the coating and fluidizing atmosphere is supplied upwardly through this passageway.
- the upper end of the tube 26 is provided with a removable closure 34 that may be mounted in any suitable manner; the closure 34 includes a central exit passageway 36 through which the fluidizing and coating gases leave the furnace enclosure and which is connected to an exit conduit 38 through which the gases may be routed for subsequent treatment if deisred.
- An injection device 40 is mounted above the closure and is designed to feed minute particles 41 into the coating enclosure at a desired rate by dropping them downward through an opening 42 in the closure where they will fall nearly the length of the tube 26 until they enter and become a part of the fluidized bed.
- Induction or alternate heating means 44 is provided for heating the active deposition region of the furnace and the particles and objects being coated to the desired deposition temperature.
- the bed of minute particles, submillimeter in size are levitated generally near the bottom of the heating enclosure in approximately the location shown in FIG. 1 by the upward flowing gas stream.
- the gas stream is usually made up of a mixture of an inert fluidizing gas plus a carbonaceous substance, such as a gaseous hydrocarbon, for example, methane, ethane, propane, butane or acetylene, or some other carbon-containing substance that is gaseous or easily vaporizable.
- a source 46 or hydrocarbon is illustrated which is equipped with a flow-regulating valve arrangement 48.
- a source 50 of inert gas for example, helium, argon or nitrogen, which is likewise equipped with a suitable flow-regulating valve arrangement 52. These two sources flow into a common line 54 which connects to the vertical passageway 32 in the insert 28.
- the total flow of the gas upward through the coating enclosure is regulated so that the fluidized bed occupies the region near the botton of the tube 26 as depicted in FIG. 1.
- the upward flow of the gaseous atmosphere through the central passageway causes a generally annular flow pattern to be established in the fluidized bed region, with the minute particles travelling upward in the central portion of the enclosure and then downward generally along the outer perimeter thereof.
- particles having a density of at least about 3 grams/cm 3 i.e., greater than the density of the carbon coating
- they will gradually become less dense as they grow in size.
- the smaller uncoated particles tends to remain in the lower portion of the bed while the less dense coated particles are levitated to the upper portion of the bed.
- a preferred material for the particles is zirconium oxide which has a density of about 5.5 grams/cm 3 .
- the weir tube 56 is provided with a hood 64 to close the upper end of the tube against the entrance of airborne particles and dust. Due to the fluidization process, there is some bubbling and splashing of the particles predominately in the central portion of the bed. When the bubbles burst, particles are sprayed generally radially with respect to the vertical axis of the bed. As the gas bubbles tends to pick up particles from adjacent the bottom of the bed, the sprayed particles tend to be the smaller, relatively thin-coated ones, and therefore, it is not desired that such particles be withdrawn. It is important that the spillover hole is positioned facing away from the central portion of the bed where the bubbling is most likely to occur.
- the collection chamber 62 is preferably pressurized with inert gas from a suitable source 66 with the rate of gas flow controlled by a value 68.
- the flow of inert gas through the collection chamber 62 and up the weir tube 56 through the exit conduit 60 acts as a purge to prevent substantial quantities of dust from falling down into the collection chamber this maintaining clear the glass walls forming the chamber to permit observation by the operator that the apparatus is functioning properly.
- the flow of inert gas does not have to be varied as it would if it were used to regulate the particle withdrawal rate as in U.S.-A-3,977,896.
- the purge gas flows at a constant, relatively slow rate sufficient to prevent movement of substantial quantities of dust into the collection chamber 62, but insufficient to prevent coated particles from falling down the weir tube 56 into the collection chamber.
- Operation of the apparatus of the present invention is as follows: A supply of particles 41, along with the object or objects to be coated, are placed in the coating enclosure and the enclosure is brought up to its operating temperature of 1,200 to 2,000 degrees Centigrade with the fluidizing gas flowing. After the operating temperature is attained, the coating gas valve is opened so that the coating gas and the fluidizing gas both flow through the input line 54. The bed level starts to rise slowly due to the particles in the bed acquiring a pyrolytic carbon coating because of the thermal decomposition of the gaseous carbonaceous substances. After a while, the injection device 40 is turned on to add seed particles 41 which increases the rate at which the bed rises.
- the apparatus 20 Upon completion of the coating process, the apparatus 20 is disassembled and the coated objects removed. It will be appreciated that the contents of the container 63 includes small and large particles. The contents can be screened and the large particles disposed of and the smaller ones recycled.
- fluidized bed apparatus of the present invention has been described in terms of applying a pyrolytic carbon coating to objects due to thermal decomposition of gaseous carbonaceous substances in the presence of the particles, it will be appreciated that the present invention is not limited to this particular use, but has utility in other applications where coatings are to be applied to particles by flowing a gas including the coating material through a bed of the particles.
Abstract
Description
- This invention relates to level control and, more particularly, to a method and apparatus for maintaining a predetermined upper level in a fluidized particle bed.
- It is desirable to deposit pyrolytic carbon coatings on certain objects. For example, uranium particles can be coated with a pyrolytic carbon which, in part, forms a pressure-retentive shell allowing the coated particles to be fabricated into fuel rods for use in nuclear reactors. Another important use for such coatings is for heart valve and other biomedical components because a pyrolytic carbon coating does not react with blood.
- Pyrolytic carbon is usually deposited on an object by thermally decomposing gaseous hydrocarbons or other carbonaceous substances in vaporous form in the presence of the object. When pyrolytic carbon is deposited in a fluidized bed apparatus, one of the variables upon which the structure of the pyrolytic carbon will be dependent is the amount of available deposition surface area relative to the volume of the furnace enclosure wherein the deposition is occurring. Pyrolytic carbon which has a microstructure that has smaller growth features will be deposited when the relative amount of deposition surface area is fairly high. Thus, when relatively large objects, for example, objects having at least one dimension equal to 5 mm. or more, are being coated, an ancillary bed of small particles (usually of a size meaasured in microns) is included within the furnace enclosure together with the larger objects. This arrangement provides sufficient available total surface area to assure that pyrolytic carbon having the desired crystalline form will be deposited. In addition, the random motion of large objects in fluidized beds provides for a relatively uniform deposition of carbon on all surfaces.
- However, whenever such submillimeter particles are being coated in a fluidized bed, the total surface area of the particles begins to increase significantly as the diameters of the pyrolytic carbon-coated particles grow. This change in the available deposition surface area in the fluidized bed will result in a change in the physical characteristics or the pyrolytic carbon being deposited if the other coating variables are held constant, e.g., coating temperature, gas flow rate and gas composition; and moreover, when the bed reaches some maximum size, it will collapse and thus limit the thickness of the carbon coating that can be deposited on levitated substrates under constant input conditions. Changes in the physical characteristics of the carbon deposited may be undesirable for any of a number of reasons.
- It has been found that pyrolytic carbon having good structural strength and uniform physical properties can be desposited as relatively thick coatings upon relatively large objects in the accompaniment of particles if the available fluidized bed surface area is maintained relatively constant by withdrawing particles which have become enlarged in size as a result of coating and feeding smaller size particles into the deposition enclosure. Commonly assigned U.S.-A-3,977,896, is directed to this type of process for depositing pyrolytic carbon coatings. In that patent the flow of gaseous atmosphere is introduced beneath and generally centrally of the particle bed. Seed particles having relatively greater densities than that of the coating are introduced to the bed causing the coated particles to levitate where they can be removed through a withdrawal tube, the open end of which is positioned near the top of the bed. The rate at which the particles are removed is controlled by regulating the rate of flow of an inert gas up the tube. The seed particle input is at a constant rate and the output is measured so that by varying the purge gas flow rate to regulate the output, a substantially constant bed total surface is achieved.
- While such a coating process works well, the need for measuring the output and varying the purge gas flow rate in response thereto introduces certain complexities which it is desirable to avoid. It has been found that in many coating applications proper coating can be achieved by maintaining the bed ata predetermined level. The fluidized bed containing process equires an operating temperature of betwen 1,200° and 2,000°. Prior art sensors for detecting bed level to control the rate of addition or removal are inoperable or unreliable under these fluidized bed operating conditions.
- We have now developed a reliable level control for fluidized bed operating at elevated temperatures. The level control of the present invention operates to substantially eliminate dust from the particle discharge pipe for the bed apparatus, which dust otherwise could interfere with the collection of withdrawn particles. The level control also functions to reduce the ratio of smaller particles to larger particles being withdrawn to enhance the coating efficiency of the fluidized bed apparatus. As the level control operates passively to achieve maintenance of a predetermined bed level, the complexity of the overall fluidized bed system is reduced because the need to weigh the output and input, and continually change a flow rate in response thereto is eliminated.
- The level control of the invention is reliable, has a long service life, and is simple to manufacture.
- Accordingly, the present invention provides a fluidized bed apparatus comprising an enclosure for containing a bed of the particles; means for causing flow of a gaseous atmosphere carrying a material for forming a coating of said particles upwards through the bed of particles to fluidize the particles, said coating having a relatively lesser density and said particles having relative greater densities; and a weir tube defined by a side wall, said means for causing flow of the gaseous atmosphere being adapted to cause the gaseous atmosphere to flow from underneath the bed and substantially centrally thereof, the weir tube being substantially vertically disposed and extending through a portion of the bed adjacent a side wall thereof; the means for causing flow of the gaseous atmosphere causing bubbling of the bed of particles above a predetermined level with the bubbling being generally confined to the central portion of the bed, which is characterised in that the weir tube extends above said bed and has a spillover entrance hole defining a maximum particle level for the bed by receiving and removing particles having substantial coatings from the bed but not removing substantial quantities of uncoated or lightly coated particles when the content of the bed achieves the level, said spillover hole facing away from the central portion, and said weir tube further comprising a hood for closing the upper end of the tube, whereby the relatively less dense coated particles levitate to the top of the bed where they are removed from the bed through the weir tube entrance hole.
- Briefly, the fluidized bed apparatus of the present invention includes an enclosure holding the bed of the particles and means for causing the upward flow of the gaseous atmosphere carrying a material for forming the coating through the bed of particles to fluidize the particles. A means for adding seed particles to the bed is provided, and a weir tube means removes coated particles from the bed when the content of the bed achieves a predetermined level. Finally, the apparatus includes a discharge means for removing the coated particles from the tube and conveying them to a collection location.
- The present invention will be further described with reference to the accompanying drawings, in which:
- .FIG. 1 is a front elevational view, partly sectional and partly schematic in nature, of the fluidized bed apparatus of the present invention, including a weir tube for use in level control;
- FIG. 2 is an enlarged longitudinal sectional view of the weir tube of FIG. 1; and
- FIG. 3 is a sectional view enlarged in size, taken generally along line 3-3 of FIG. 1 depicting the angular orientation of the spillover hole of the weir tube with respect to the central portion of the fluidized bed.
- Corresponding reference characters indicate corresponding components throughout the several views of the drawings.
- Referring now to the drawings, fluidized bed apparatus for applying a pyrolytic carbon coating to objects, is generally indicated by
reference character 20. The apparatus includes afurnace 22 having a cylindricalouter shell 24. Thefurnace shell 24 supports the coating enclosure which is defined by atube 26 having aninsert 28 affixed thereto at its lower end. Theinsert 28 provides the internal coating enclosure withconical bottom surface 30. Acentral passageway 32 extends vertically upward through theinsert 28, coaxial with thetube 26, and the coating and fluidizing atmosphere is supplied upwardly through this passageway. - The upper end of the
tube 26 is provided with aremovable closure 34 that may be mounted in any suitable manner; theclosure 34 includes acentral exit passageway 36 through which the fluidizing and coating gases leave the furnace enclosure and which is connected to anexit conduit 38 through which the gases may be routed for subsequent treatment if deisred. Aninjection device 40 is mounted above the closure and is designed to feedminute particles 41 into the coating enclosure at a desired rate by dropping them downward through anopening 42 in the closure where they will fall nearly the length of thetube 26 until they enter and become a part of the fluidized bed. Induction or alternate heating means 44, is provided for heating the active deposition region of the furnace and the particles and objects being coated to the desired deposition temperature. - In the fluidized
bed coating apparatus 20, sometimes referred to hereinafter as a "steady-state bed", the bed of minute particles, submillimeter in size, are levitated generally near the bottom of the heating enclosure in approximately the location shown in FIG. 1 by the upward flowing gas stream. The gas stream is usually made up of a mixture of an inert fluidizing gas plus a carbonaceous substance, such as a gaseous hydrocarbon, for example, methane, ethane, propane, butane or acetylene, or some other carbon-containing substance that is gaseous or easily vaporizable. In FIG. 1, asource 46 or hydrocarbon is illustrated which is equipped with a flow-regulatingvalve arrangement 48. Also illustrated is asource 50 of inert gas, for example, helium, argon or nitrogen, which is likewise equipped with a suitable flow-regulatingvalve arrangement 52. These two sources flow into acommon line 54 which connects to thevertical passageway 32 in theinsert 28. - The total flow of the gas upward through the coating enclosure is regulated so that the fluidized bed occupies the region near the botton of the
tube 26 as depicted in FIG. 1. The upward flow of the gaseous atmosphere through the central passageway causes a generally annular flow pattern to be established in the fluidized bed region, with the minute particles travelling upward in the central portion of the enclosure and then downward generally along the outer perimeter thereof. When particles having a density of at least about 3 grams/cm3 (i.e., greater than the density of the carbon coating) are used, they will gradually become less dense as they grow in size. The smaller uncoated particles tends to remain in the lower portion of the bed while the less dense coated particles are levitated to the upper portion of the bed. A preferred material for the particles is zirconium oxide which has a density of about 5.5 grams/cm3. - A
weir tube 56, formed of a refractory material, such as graphite or mullite, extends through a vertical hole in the enclosure insert 28 and through a portion of the bed of particles and thereabove adjacent a side of the bed. A spillover hole orentrance 58 in thetube 56 defines a predetermined maximum level L for the bed of particles. When this level is reached, the continuous addition of seed particles in concert with the fluidization of the bed caused by the upward flowing gas stream results in withdrawal of particles having substantial coating thicknesses. Anexit conduit 60 receives the withdrawn particles from theweir tube 56 and channels them into acollection chamber 62 where they are received in acontainer 63. - Referring to FIGS. 2 and 3, the
weir tube 56 is provided with ahood 64 to close the upper end of the tube against the entrance of airborne particles and dust. Due to the fluidization process, there is some bubbling and splashing of the particles predominately in the central portion of the bed. When the bubbles burst, particles are sprayed generally radially with respect to the vertical axis of the bed. As the gas bubbles tends to pick up particles from adjacent the bottom of the bed, the sprayed particles tend to be the smaller, relatively thin-coated ones, and therefore, it is not desired that such particles be withdrawn. It is important that the spillover hole is positioned facing away from the central portion of the bed where the bubbling is most likely to occur. More specifically, the spillover hole should face at ninety degrees or greater with respect to the radius intersecting the axis of the weir tube. Furthermore, the weir tube is preferably disposed away from the axis of the bed by a distance equal to at least two-thirds of the spacing between the bed axis and thetube 26. Since the particles which become airborne due to bubbling of the bed do not travel circumferentially, the positioning of thespillover hole 58 facing away from the central portion of the bed, substantially eliminates the entrance of airborne particles in the spillover hole. - The
collection chamber 62 is preferably pressurized with inert gas from asuitable source 66 with the rate of gas flow controlled by avalue 68. The flow of inert gas through thecollection chamber 62 and up theweir tube 56 through theexit conduit 60 acts as a purge to prevent substantial quantities of dust from falling down into the collection chamber this maintaining clear the glass walls forming the chamber to permit observation by the operator that the apparatus is functioning properly. It will be appreciated that the flow of inert gas does not have to be varied as it would if it were used to regulate the particle withdrawal rate as in U.S.-A-3,977,896. Here the purge gas flows at a constant, relatively slow rate sufficient to prevent movement of substantial quantities of dust into thecollection chamber 62, but insufficient to prevent coated particles from falling down theweir tube 56 into the collection chamber. - Operation of the apparatus of the present invention is as follows: A supply of
particles 41, along with the object or objects to be coated, are placed in the coating enclosure and the enclosure is brought up to its operating temperature of 1,200 to 2,000 degrees Centigrade with the fluidizing gas flowing. After the operating temperature is attained, the coating gas valve is opened so that the coating gas and the fluidizing gas both flow through theinput line 54. The bed level starts to rise slowly due to the particles in the bed acquiring a pyrolytic carbon coating because of the thermal decomposition of the gaseous carbonaceous substances. After a while, theinjection device 40 is turned on to addseed particles 41 which increases the rate at which the bed rises. There is also bubbling of the fluidized particles in the central region of the bed above the location of the centralgas inlet passageway 32. Although such bubbling and splashing causes particle movement above the predetermined level L established by the position of thespillover hole 58 in the weir tube, such airborne particles cannot enter the tube in significant quantity because the spillover hole faces away from the central bed region. Of course, the circulation provided by the fluidization causes the less dense coated particles to levitate with the just added seed particles and only lightly coated particles, which have greater densities, more likely to remain near the bottom of the bed. When the bed level reaches thespillover hole 58, particles enter the hole where they fall down thetube 56, through theexit conduit 60 and are collected in the container 67 disposed inchamber 62. The provision ofhood 64 and the slow purge of inert gas up theweir tube 56 ensure that the major portion of dust is removed through theexit conduit 38 and does not travel with the particles through the weir tube. - Upon completion of the coating process, the
apparatus 20 is disassembled and the coated objects removed. It will be appreciated that the contents of thecontainer 63 includes small and large particles. The contents can be screened and the large particles disposed of and the smaller ones recycled. - While the fluidized bed apparatus of the present invention has been described in terms of applying a pyrolytic carbon coating to objects due to thermal decomposition of gaseous carbonaceous substances in the presence of the particles, it will be appreciated that the present invention is not limited to this particular use, but has utility in other applications where coatings are to be applied to particles by flowing a gas including the coating material through a bed of the particles.
- As a method of providing level control for fluidized bed apparatus used in applying a coating having a relatively lesser density to particles having relatively greater densities by causing the passage of a gaseous atmosphere through a bed of the particles, the present invention comprises the following steps:
- A) A substantially vertical weir tube is provided extending through a portion of the particle bed and thereabove adjacent a side of the bed.
- B) A spillover hole is provided in the tube disposed to define a predetermined level of the bed.
- C) The hole is angularly positioned so that it faces away from a central portion of the bed.
- D) The upper end of the tube is covered and the tube is purged at a substantially constant flow rate sufficient to prevent a substantial quantity of dustfrom moving down the tube but insufficient to prevent coated particles from moving down the tube.
- In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.
Claims (6)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT85302874T ATE34089T1 (en) | 1984-04-26 | 1985-04-24 | LEVEL CONTROL FOR A FLUIDIZED BED. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US604028 | 1984-04-26 | ||
US06/604,028 US4546012A (en) | 1984-04-26 | 1984-04-26 | Level control for a fluidized bed |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0162599A1 EP0162599A1 (en) | 1985-11-27 |
EP0162599B1 true EP0162599B1 (en) | 1988-05-11 |
Family
ID=24417891
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP85302874A Expired EP0162599B1 (en) | 1984-04-26 | 1985-04-24 | Level control for a fluidized bed |
Country Status (8)
Country | Link |
---|---|
US (1) | US4546012A (en) |
EP (1) | EP0162599B1 (en) |
JP (1) | JPS60238130A (en) |
AT (1) | ATE34089T1 (en) |
AU (1) | AU572986B2 (en) |
CA (1) | CA1235893A (en) |
DE (1) | DE3562563D1 (en) |
IE (1) | IE56224B1 (en) |
Families Citing this family (59)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5387247A (en) * | 1983-10-25 | 1995-02-07 | Sorin Biomedia S.P.A. | Prosthetic device having a biocompatible carbon film thereon and a method of and apparatus for forming such device |
US5084151A (en) * | 1985-11-26 | 1992-01-28 | Sorin Biomedica S.P.A. | Method and apparatus for forming prosthetic device having a biocompatible carbon film thereon |
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DE2721182A1 (en) * | 1977-05-11 | 1978-11-23 | Nukem Gmbh | FLUID BED REACTOR FOR PROCESSING CARBON-COATED PARTICLES |
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1984
- 1984-04-26 US US06/604,028 patent/US4546012A/en not_active Expired - Lifetime
-
1985
- 1985-04-01 CA CA000478060A patent/CA1235893A/en not_active Expired
- 1985-04-02 IE IE843/85A patent/IE56224B1/en unknown
- 1985-04-17 AU AU41334/85A patent/AU572986B2/en not_active Ceased
- 1985-04-24 AT AT85302874T patent/ATE34089T1/en active
- 1985-04-24 DE DE8585302874T patent/DE3562563D1/en not_active Expired
- 1985-04-24 EP EP85302874A patent/EP0162599B1/en not_active Expired
- 1985-04-26 JP JP60090761A patent/JPS60238130A/en active Pending
Non-Patent Citations (1)
Title |
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Ullmanns Encyclopädie der technischen Chemie, 4th ed: Vol. (3) (1980), pages 434, 435, 453,456 * |
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JPS60238130A (en) | 1985-11-27 |
US4546012A (en) | 1985-10-08 |
DE3562563D1 (en) | 1988-06-16 |
ATE34089T1 (en) | 1988-05-15 |
CA1235893A (en) | 1988-05-03 |
EP0162599A1 (en) | 1985-11-27 |
AU4133485A (en) | 1985-10-31 |
AU572986B2 (en) | 1988-05-19 |
IE850843L (en) | 1985-10-26 |
IE56224B1 (en) | 1991-05-22 |
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